DE19620720C1 - Exhaust gas desulphurising - Google Patents

Abstract

To operate the desulphurising unit, for exhaust gases at a power station using fossil fuels, the suspension produced with water enriched by sulphates is treated with a quicklime with a high burning rate which on slaking gives a temp. development of 60 deg after more than 8 minutes.

Description

The invention relates to a method for operating a Flue gas desulfurization plant in a fossil fuel-fired one Power plant in which a suspension of the desulfurization produced sulfate-enriched water or cooling tower waste water and quicklime is manufactured and the gas scrubber Flue gas desulfurization system is introduced into the SO₂-containing flue gases (Wet process).

The use of the sulfate enriched produced during desulfurization Water or the cooling tower waste water in a cycle process for the production a suspension of limestone and water is, for example, from the DE 37 14 092 known. The advantage is that with a satisfactory one Desulfurization level the sulfate-enriched water is reused and thus the water balance of the flue gas desulfurization system is not affected. The disadvantage, however, is that the limestone's relatively low reactivity to a high limestone requirement as well as higher plant and operating expenses leads.

A reduction in the effort was achieved in that for the production of Suspension quicklime was used as it significantly improved Reactivity and favorable stoichiometry occur during the desulfurization process and the carbon dioxide content from the limestone does not have to be transported.

So far, however, the use of quicklime requires quicklime either with fresh water (low sulfate water) must be extinguished (G. Pohl: "On the influence of SO₄ ions in the extinguishing of white lime", ZKG 8 (1955), P. 393), which in addition to the need for water for rinsing processes in the  Flue gas desulphurization caused an additional water requirement, or at Use sulfate-enriched water to extinguish the quicklime Groats occur.

For this reason, water with a sulfate content greater than 300 mg / l must be extinguished was classified as unsuitable by quicklime (U. Wittneben: "Investigations the particle properties of suspended lime hydrates ", ZKG, 10 (1980) p. 26).

In contrast, it was proven in DE 44 02 773 A1 that the use of Lime hydrate suspensions from sulfate-enriched water and quicklime for SO₂ separation in wet flue gas scrubbing despite the occurring Grimacing is basically possible. For largely wastewater-free Flue gas desulfurization technology is then used is extinguished with the sulphate-enriched water circulated and diluted to suspension in a manner known per se in the swamp of the Gas scrubber is introduced. The reaction mechanisms that occur cause a coarsening (grits) of the grain spectrum of the suspension. To improve the reactivity, these grains have to be and energy-intensive measures are removed from the suspension again. A disadvantage of this solution is also that harmful amounts in the REA gypsum are entered, which then has a high pH <pH 9. This makes the use of the REA plaster as a natural stone plaster essential restricted or made impossible. The hydrated lime discharged as semolina naturally takes part in the chemical conversion with the SO₂ of the flue gas part, which increases the amount of absorbent. The greetings did, however not the same reactivity of finely divided white lime hydrates. Therefore, the Ensuring the required efficiency of the flue gas desulfurization system the operating costs of the flue gas desulfurization system can be increased.

The present invention is therefore based on the object of a method to operate a flue gas desulfurization system for one with fossil To develop fuel-fired power plants, avoiding one Grits and maintaining the reactivity from the desulfurization generated sulfate-enriched water and quicklime a suspension for  Introduction into the flue gas desulfurization system via a gas scrubber SO₂-containing flue gases can be produced.

According to the invention the object is achieved in that in a method for Operating a flue gas desulphurization plant in one with fossil fuels fired power plant a suspension of the desulfurization generated sulfate-enriched water and quicklime is produced and over a Gas scrubber of the flue gas desulfurization system into the SO₂-containing flue gases is introduced, which in the manufacture of the suspension sulfate-enriched water is a pure lime with a high degree of burning, which Extinguish a temperature development of 60 ° according to the test method according to DIN 1060 after more than 8 minutes, is added.

Completely surprising and contrary to the prevailing view, it was found that the harmful entry of not for SO₂ separation in the flue gas used lime in REA gypsum, the higher the degree of firing for is the production of the lime hydrate suspension used in its entirety. The invention ensures that when using sulfate-rich water no harmful groats occur and a high reactivity of the manufactured suspension is guaranteed.

With the solution according to the invention, the operating expenditure can be significant can be minimized, since additional measures to remove the groats in the REA gypsum is no longer required. Gypsum recycling is therefore possible without restrictions and the water balance of the power plant is improved.

The invention will be explained in more detail below using an exemplary embodiment will.

In the drawing, the

Fig. 1 is a system diagram for the flue gas desulfurization of a power plant fired with fossil fuels.

The flue gas desulfurization system comprises the gas scrubber 1 with flushing water line 2 , flue gas duct 3 , clean gas duct 4 and the gas scrubber suspension line 11 and the oxidation air line 12 . The gas scrubber 1 is connected via line 5 to the complex of quicklime extinguishing system, suspension receiver and metering device 6 via line 7 to the gypsum drainage and FGD water discharge.

The quicklime slaking system, suspension system and metering device 6 are connected via the conveyor system 13 to the storage container 14 and via line 15 to the circulating water container 10 (cooling tower drainage system or the internal sulfate precipitation).

The mode of action is as follows:
The quicklime 22 is conveyed from the reservoir 14 via the conveyor system 13 into the quicklime-extinguishing system, suspension template and metering device 6 and through the pumped via line 15 sulfate enriched Kühlturmabflutwasser (circulation water) 23 with a sulphate content) 300 mg / l from the Kühlturmabflutsystem 10 and Sulphate-rich, conditioned REA cycle water conveyed via line 17 is extinguished from the internal sulphate precipitation with a sulphate content of <300 mg / l. These sulfate-enriched waters are used to prepare the suspension 24 . The suspension 24 is conveyed into the gas scrubber 1 via the line 5 .

The following reactions occur:

• 1. quicklime 22 with sulfate-enriched cycle water GaO + H₂O → Ca (OH) ₂
• 2. The offset with the suspension 24 suspension scrubber 25 with oxidizing air 27 and combustion gas 26th . . Ca (OH) ₂ + 1 / 20₂ + SO₂ → CaSO₄ + H₂O

According to the invention, there is no occurrence in the procedure described above undesirable grit formation of the suspension when single-grade limes are used be that have a degree of burning that when extinguishing a Temperature development of 60 ° after more than 8 minutes shows and no shares with lower degree of firing is contained in the lime.  

The invention uses sulfate-rich water for the production the lime suspension possible without adverse effects on the REA gypsum, whereby the water balance of the power plant is improved by the Water withdrawal is reduced and the amount of wastewater is reduced. The REA gypsum is fully usable because of its low pH or a low alkalinity is maintained.

No unused Ca (OH) ₂ is discharged in the form of grit. The High reactivity of the suspension produced is due to the use of quicklime secured. The operating effort is reduced by the invention.

Reference list

1 gas washer
2 rinse water pipe
3 flue gas duct
4 clean gas channel
5 line
6 quicklime extinguishing system, suspension template and dosing device
7 line
8 hydrocyclone
9 line
10 circulating water tanks
11 Gas scrubber suspension line
12 Oxidation air line
13 conveyor system
14 storage containers
15 line
16 upper reaches
17 line
18 management
19 band filter
20 line
21 screw conveyor
22 quicklime
23 circulating water
24 suspension
25 laundry suspension
26 flue gas
27 Oxidation air
28 rinse water
29 reaction product
30 water
31 gypsum sludge
32 water
33 plaster
34 flue gas

Claims (1)

A method for operating a flue gas desulfurization system in a power plant fired with fossil fuels, in which a suspension is produced from sulfate-enriched water generated during the desulfurization or cooling tower waste water and quicklime and is introduced into the SO₂-containing flue gases via a gas scrubber of the flue gas desulfurization system, characterized in that During the preparation of the suspension, a lime with a high degree of burning, which exhibits a temperature development of 60 ° after more than 8 minutes, is added to the sulfate-enriched water.